RF electron beam accelerators have found wide usage in medical accelerators where the accelerated high energy electron beam is employed to generate x-rays for therapeutic and diagnostic purposes. Electron beams generated by an electron beam accelerator can also be used directly or indirectly to kill infectious agents and pests, to sterilize objects, to change physical properties of objects, and to perform testing and inspection of objects, such as containers, containers storing radioactive material, and concrete structures.
In radiofrequency (RF) accelerators, particle acceleration may be powered by feeding RF power into the accelerator cavities. The accelerating cavities may have a loaded Q value of a few thousands to more than ten thousands. The resonance frequency of acceleration may drift with heating, and the RF source frequency may be “tuned” (e.g., adjusted with a servo) to match frequency of the cavities. When the accelerator is operated with a magnetron, the tuning action may be accomplished by adjusting the frequency tuner. When the accelerator is operated with a klystron, the tuning action may be accomplished by adjusting the frequency control voltage of the voltage controlled oscillator (VCO) in the RF driver.
In either case, the RF source is assumed to work properly. The desired RF spectrum has most power at cavity frequency, with small amplitude side lobes. When the RF source produces RF power but its spectrum becomes bad (e.g., main lobe has lower amplitude and wide peak width), existing RF power monitors may not be able to identify the problem. While the RF source may still produce RF power output, the spectral quality of the output will have a deteriorated quality. In some cases, a sophisticated spectrum analyzer may be used for off-line diagnosis of such problem. Such off-line spectrum analyzer is configured to measure the RF spectra from the RF source. It is expensive and complicated to use, and may not be readily available in some cases.